Isoprene (2-methyl-buta-1,3-diene) is an important organic compound that is used in a wide array of applications. For instance, isoprene is employed as an intermediate or a starting material in the synthesis of numerous chemical compositions and polymers. Isoprene is also an important biological material that is synthesized naturally by many plants and animals, including humans. Isoprene is a colorless liquid at room temperature and is highly flammable.
Isoprene became an important monomer for utilization in the synthesis of cis-1,4-polybutadiene when its stereo-regulated polymerization became commercially possible in the early 1960s. cis-1,4-Polyisoprene made by such stereo-regulated polymerizations is similar in structure and properties to natural rubber. Even though it is not identical to natural rubber it can be used as a substitute for natural rubber in many applications. For instance, synthetic cis-1,4-polyisoprene rubber is widely used in manufacturing tires and other rubber products. This demand for synthetic cis-1,4-polyisoprene rubber consumes a majority of the isoprene available in the worldwide market. The remaining isoprene is used in making other synthetic rubbers, block copolymers, and other chemical products. For instance, isoprene is used in making butadiene-isoprene rubbers, styrene-isoprene copolymer rubbers, styrene-isoprene-butadiene rubbers, styrene-isoprene-styrene block copolymers, and styrene-isoprene block copolymers.
Over the years many synthesis routes for producing isoprene have been investigated. For instance, the synthesis of isoprene by reacting isobutylene with formaldehyde in the presence of a catalyst is described in U.S. Pat. No. 3,146,278, U.S. Pat. No. 3,437,711, U.S. Pat. No. 3,621,072, U.S. Pat. No. 3,662,016, U.S. Pat. No. 3,972,955, U.S. Pat. No. 4,000,209, U.S. Pat. No. 4,014,952, U.S. Pat. No. 4,067,923, and U.S. Pat. No. 4,511,751. U.S. Pat. No. 3,574,780 discloses another process for the manufacture of isoprene by passing a mixture of methyl-tert-butyl ether and air over mixed oxide catalysts. The methyl-tert-butyl ether is then cracked into isobutylene and methanol over the catalyst. The methanol produced is oxidized into formaldehyde which then reacts with the isobutylene over the same catalyst to produce the isoprene. U.S. Pat. No. 5,177,290 discloses a process for producing dienes, including isoprene, which involves reacting a reaction mixture of a tertiary alkyl ether and a source of oxygen over two functionally distinct catalysts under reaction conditions sufficient to produce high yields of the dienes with minimal recycle of the ether.
The isoprene used in industrial applications is typically produced as a by-product of the thermal cracking of petroleum or naphtha or is otherwise extracted from petrochemical streams. This is a relatively expensive energy-intensive process. With the worldwide demand for petrochemical based products constantly increasing, the cost of isoprene is expected to rise to much higher levels in the long-term and its availability is limited in any case. In other words, there is a concern that future supplies of isoprene from petrochemical based sources will be inadequate to meet projected needs and that prices will rise to unprecedented levels. Accordingly, there is a current need to procure a source of isoprene from a low cost, renewable source which is environmentally friendly.
In addition, isoprene produced from petrochemical feedstocks requires extensive purification before it can be converted to polymers. Cost effective methods are desirable for producing highly pure isoprene from renewable resources and converting it to polyisoprene products taking advantage of the high purity and/or the unique impurity profiles of bioisoprene compositions.
The invention described herein fulfills these needs and provides additional benefits as well.